Field of the Invention
The present invention is related to magneto-thermoelectric generator devices. More particularly, the present invention is related to magneto-thermoelectric generator devices with improved mechanical energy that can be used to harvest waste heat.
Description of Related Art
Many inventions and significant research show the vast efforts to meaningfully harvest waste thermal energy. In some cases, excess thermal energy is simply removed to provide for lower operational temperatures of systems or components. This active cooling can sometimes achieve a net gain in system efficiency (e.g. active cooling of concentrated solar cells), but ultimately requires the input of adequate energy to move a cooling fluid. Other research has focused on the conversion of thermal energy into electrical energy that may be used instantaneously, or stored in batteries or capacitors for later use. Thermoelectric Peltier or Seebeck effect devices operate to harvest electricity from thermal gradients, as do magnetothermoelectric generators.
Photovoltaic (PV) power is increasingly gaining a greater share as a source of power production in developed countries, and is becoming a principal source of power for Unmanned Aerial Vehicles (UAVs), particularly those requiring long durations of flight such as High Altitude Long Endurance (HALE) air vehicles. HALE air vehicles have the potential to meet a long standing need for both military and non-military operations where persistent intelligence, surveillance, and reconnaissance (ISR) capabilities are required. Military operators need a reliable capability which can be quickly deployed to emerging theatres, and commercial operators desire these long endurance platforms for communication hubs and environmental monitoring. In recent years the enabling technologies required for solar powered High Altitude Long Endurance (HALE) air vehicles have matured to where missions requiring months to years of flight duration, such as the DARPA Vulture and the Air Force ISIS, are becoming feasible.
HALE platforms come in various shapes and sizes ranging from small hand-launched unmanned aerial systems (UAS's) such as the AF Solar Raven to very large high aspect ratio aircraft such as NASA's Helios to Lighter than Air (LTA) vehicles such as the Air Force ISIS, Lockheed Martin's High Altitude Airship (HAA), or the Army's Long-Endurance Multi-Intelligence Vehicle (LEMV). One thing most of these vehicles have in common is that they will utilize solar cells to achieve long times on station. However, energy production remains the limiting factor to achieving payload and longer endurance. Additional energy in the form of heat is available on these vehicles due to PV cells, high power RF, propulsion systems, and energy storage to name the most common. Thus, thermal management aboard these vehicles is becoming more critical as high power payloads become standard. In addition, PV power production is limited by temperature-dependent reductions in efficiency of photovoltaic cells. Thus, a device that can scavenge heat from a PV cell and convert it to electrical energy can significantly improve power to the overall system.
Previously, Ujihara and colleagues described an energy harvesting apparatus that may include a ferromagnetic material and/or a shape memory alloy to convert thermal energy to mechanical energy to electrical energy (U.S. Pat. No. 7,800,278 (see also International Patent Application Publication No. WO2007/087383), which patent and publication are incorporated by reference herein in their entireties). The apparatus is subjected to a thermal gradient to cause beams to bend thus creating stress/strain in a piezoelectric material. However, for such a system, the output power is the product of the mechanical energy, the operational frequency, and the mechanical to electrical conversion of the harvesting springs. Additionally, others have described devices for converting heat to electrical energy, but which do not entertain an intermediate conversion step of converting the thermal energy to mechanical energy, such as is disclosed in U.S. Pat. No. 3,664,881, which patent is incorporated by reference herein in its entirety.
Thus, any improvement in mechanical energy of such systems will result in a proportional increase in power output. To date, there remains a need for improvement in the power output of magnetothermoelectric generators as well as a need for applications of magnetothermoelectric generators for converting waste heat from photovoltaic cells into power.